The present invention relates to a semiconductor device technique and particularly to a technique applicable effectively to the improvement in whisker resistance of lead-free plating.
In connection with a semiconductor integrated circuit device there is known a structure in which an alloy layer higher in melting point than tin-lead eutectic solder and not containing lead as a principal constituent metal is formed in a portion outside a resin-sealed portion (see, for example, Patent Document 1).
Recently, with consideration for environment, the use of lead has been diminished and the application of lead-free plating has been increasing. Lead-free plating has come to be used widely as surface treatment for external terminals in semiconductor devices, etc.
In lead-free plating, however, there exists a problem of growth of tin whisker as a latent problem. The occurrence of tin whisker is a natural phenomenon difficult to suppress and is presumed to be caused by natural standing, temperature cycle, or corrosion in a high-temperature high-humidity environment. Particularly, the whisker based on temperature cycle occurs in common in case of tin being contained irrespective of the type of plating.
There are various causes of tin whisker occurrence, but it is presumed that tin whisker is caused by the application of a compressive stress to a plating film, resulting in the plating film being pushed out. Most of the measures for remedying tin whisker are such countermeasures as baking and reflowing, with no effective remedial measure having been found out in exterior treatment.
On the other hand, against whisker caused by fitting of a connector product or the like, plural-layer plating using different kinds of metals or plural-layer plating using different types of platings has been proposed as one of remedial measures.
The present invention has been studied and accomplished under the technical background of suppressing and remedying the growth of tin whisker in lead-free plating which whisker growth has heretofore been a latent problem as mentioned above.